All emails sent by me since January 2017 are signed using PGP, that's why they have an attached text file called "signature.asc", it's just a text plain file containing my digital signature of that particular email.

Using this file and my public PGP key, your email client should be able to check that it was really me who wrote the email and it wasn't modified afterwards, also it makes it possible to send me encrypted messages in case you think it's needed.

You can find my public PGP key in this key server among others, and also it can be downloaded from the following links: